Since the discovery of new mineral oil reservoirs is becoming increasingly difficult and the development thereof is becoming ever more expensive, ways of increasing the yield from reservoirs already in production are being sought. These include, for example, flooding with water and, in more recent times, flooding with formulations comprising nanoparticles. Especially formulations containing silicon dioxide are the focus of attention because of their environmental compatibility.
WO2014/020061 describes a method of producing mineral oil in which a shear-thickening formulation of polyethylene oxide, water and particular hydrophobic silica particles is used. This formulation exhibits thickening at moderate shear rates and thinning at high shear rates. This is said to enable simpler introduction of the formulation into the mineral oil deposit. However, the formulation described has limited stability in solutions having a high salt concentration, for instance seawater.
US2015075798 describes a method of producing mineral oil, in which a dispersion comprising hydrophobically modified polyacrylamide particles (HMPAM) and particles of a silica, for example a fumed silica, is used. The combination of particles is said to be more effective than a dispersion containing either only HMPAM or only silica.
Aurand et al., in International Symposium of the Society of Core Analysts, Avignon, France, Sep. 8-11, 2014 (SCA2014-017), report their results relating to EOR applications of nanostructured fumed silica particles and colloidal silica particles. According to these, the fumed particles show advantages. However, adsorption data and the rising pressure during the experiments point more to a mechanical effect of the fumed particles than to a chemical mechanism, such as the log-jamming of the particles on the rock.
Abbas Roustaei et al. report in Egyptian Journal of Petroleum (2013) 22, 427-433 report on the capability of silica particles to alter the wettability of the reservoir rock and reduce the interfacial tension between crude oil and brine phases. Fumed silica AEROSIL® R 816, Evonik Industries, was used, which is obtained by surface-modifying AEROSIL® 200, Evonik Industries, using hexadecylsilane. Fumed silica AEROSIL® R 816 is only partially hydrophilic. Fluids, 1-4 g/L of fumed silica AEROSIL® R 816 in ethanol were prepared by sonication.
US2003/220204 discloses a method of recovering oil comprising the step of injecting a foamable fluid, the fluid comprising surface-modified nanoparticles. The nanoparticles are selected from the group consisting of silica, titania, alumina, zirconia, vanadia, ceria, iron oxide, antimony oxide, tin oxide, alumina/silica, and combinations thereof. The nanoparticles can be surface-modified to obtain a non-polar or a polar surface-modified nanoparticle. Suitable surface-modifying substrates are silanes selected from group consisting of alkylchlorosilanes, alkoxysilanes, trialkoxyarylsilanes, silane functional (meth)acrylates and polydialkylsiloxanes.